1. Field of the Invention
The present invention relates in general to a catalytic converter incorporated in an automotive exhaust system, and more particularly to a catalytic converter which has an electrically resistive catalyst support for heating a catalyst up to operating temperature by electrical energy.
2. Description of the Prior Art
U.S. Pat. No. 3,770,389 discloses a catalytic converter for transforming noxious emissions into harmless carbon dioxide and water vapor. The catalytic converter has an electrically resistive catalyst support for heating the catalyst up to an operating temperature where the catalyst begins catalytic activity by electrical energy. The catalyst support comprises a corrugated stainless steel sheet and a flat stainless steel sheet which are sandwiched together and wound spirally. Both sheets are coated with thin coatings of an electrically insulating ceramic material in which catalyst particles are uniformly dispersed. Both sheets are connected to an external electric power source. Thus, upon energization, the electric current flows spirally through the sheets against a high electrical resistance possessed by the spirally wound stainless steel sheets. Thus, the catalyst is heated up to its operating temperature within a short time after an engine is started.
However, the conventional catalytic converters of the above-mentioned type have the following drawback.
That is, during manufacturing and/or use of them, it tends to occur that the electrically insulating coatings on the stainless steel sheets peel off from the sheets. This induces a short circuit between neighboring layers of the stainless sheets and thus lowers the electric resistance of the catalyst support. With this reduced electric resistance, the catalyst support can not be heated up to a degree sufficient for heating the catalyst to the operating temperature.